The present invention relates to an image data transmitting/receiving apparatus incorporated in an electronic copy machine having a copy function, a printer function, etc.
It is generally known that a multi-purpose apparatus fulfilling a facsimile function, a copy function, a printer function, and the like has a so-called memory transmission mode in which an image read by a scanner is stored once in a memory and its corresponding image data is transmitted.
Under the ITU's (International Telecommunications Union) recommendation, in the facsimile function of the multi-purpose apparatus, an A4-sized document is usually placed lengthways toward the scanner (referred to as "in A4-R direction" which means that the scanning distance of the scanner in the subscanning direction is longer than that in the main scanning direction), and an image is read therefrom and transmitted.
A long scanning time is required to read an image from the A4-sized document placed in the A4-R direction. Conventionally, therefore, when an image is read out from the A4-sized document placed widthways toward the scanner (referred to as "in A4-Y direction" which means that the scanning distance of the scanner in the main scanning direction is longer than that in the subscanning direction), it is transmitted as data for an A3-sized sheet. However, the reception of image in A3 size is one option, and there are many cases where a receiver is unable to receive image data in size of A3. In these cases, the read image data has only to be rotated. For example, if image data read from an A4-sized document set in the A4-Y direction is rotated 90.degree. (or 270.degree.), its direction will be the same as that of image data read in the A4-R direction on the ITU's recommendation.
However, in order to rotate an image whose resolution varies between the main scanning and subscanning, the resolution need to be changed and the image may be degraded accordingly. For example, an image, which is read by main scanning 1 (resolution 8 lines/mm) indicated by arrow a and subscanning 1 (resolution 15.4 lines/mm) indicated by arrow b, as shown in FIG. 7A, is rotated and converted into an image of main scanning 2 (resolution 8 lines/mm) and subscanning 2 (resolution 15.4 lines/mm), as shown in FIG. 7B. In actuality, the image has to be reduced 52% (8/15.4) from subscanning 1 to main scanning 2 and enlarged 192% (15.4/8) from main scanning 1 to subscanning 2. When the image is reduced 52% as illustrated in FIGS. 7C and 7D, an image is degraded due to a missing line or the like. To prevent this, a line holding circuit can be added, but the cost is increased.
As described above, the conventional apparatus has the drawback wherein if an image read from a document scanned in the A4-Y direction by a scanner is facsimiled in the A4-R direction based on the ITU's recommendation, the image is degraded when it is rotated.